The Long Term Evolution (LTE) of the Universal Mobile Telecommunication System (UMTS) technology has been a major new technology research and development item initiated by the 3rd Generation Partnership Project (3GPP) in recent years. This technology can be regarded as a “quasi-4G technology”. The LTE-Advanced (LTE-A) has been subsequent evolvement of the LTE. The 3GPP finalized the technical demand report of the LTE-A in 2008 and proposed the lowest demands of the LTE-A: a downlink peak rate of 1 Gbps and an uplink peak rate of 500 Mbps with spectrum utilization ratios of 15 Mbps/Hz and 30 Mbps/Hz respectively at the uplink and downlink peaks. In order to satisfy the various demand indexes of the 4G technology, the 3GPP has proposed several crucial technologies for the LTE-A, including, for example, carrier aggregation, coordinated multi-point transmission and reception, multi-antenna enhancement, etc.
The existing LTE system has approximated to the Shannon limit in terms of its frequency band utilization ratio. The throughput of the system has to be improved by improving the bandwidth or the signal to noise ratio of the system. In order to satisfy the peak rate requirement, the LTE-A currently supports a bandwidth of 100 MHz, but it may be difficult to locate such a large bandwidth among existing available spectrum resources and such large bandwidth brings great difficulty to the hardware design of a base station and a terminal. An economic and effective solution is Carrier Aggregation (CA), where for example at most 5 idle carriers are allocated to a User Equipment (UE) for availability of a larger transmission bandwidth. For example, 5 carriers with a bandwidth of 20 MHz can be aggregated into 100 MHz to serve a UE collectively.
At present the Evolved Universal Terrestrial Radio Access (E-UTRA) system supports 6 channel bandwidths: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz.
Downlink Control Information (DCI) including control information about resource allocation and other aspects of one or more User Equipments (UEs) is carried over a Physical Downlink Control Channel (PDCCH) of a carrier. In the LTE, both unlink and downlink resource scheduling information is carried over a PDCCH. In general, a plurality of PDCCHs may be present in a sub-frame. The user has to firstly demodulate the DCI over the PDCCH and then demodulate its own Physical Downlink Shared Channel (PDSCH) (including a broadcast message, paging, data of the UE, etc.) at a corresponding resource position.
In a heterogeneous network scenario with carrier aggregation, for example, resources are typically scheduled through cross-carrier scheduling to lower interference. In cross-carrier scheduling, a UE needs to parse a PDCCH over only one scheduling carrier, e.g., a primary carrier, and the UE also needs to parse the PDCCH for information about resource allocation over a scheduled carrier, e.g., a secondary carrier. Thus in cross-carrier scheduling, DCI information carried in the PDCCH of the scheduling carrier may be more complex (including both the DCI of the scheduling carrier and DCI of all the scheduled carriers). In view of this, a Carrier Indicator Field (CIF) may be further added to a DCI format to indicate the number of a scheduled carrier corresponding to the CIF. At present a CIF in the 3GPP standard is information at a fixed length of 3 bits. In the case that 5 component carriers are allocated to a UE for transmission, if a PDCCH of one scheduling carrier carries control information about all the other 4 carriers, then 5 pieces of DCI and corresponding CIF fields have to be involved. Apparently in the case of cross-carrier scheduling, the UE has to detect blindly in a search space with an increase in complexity, and a larger control channel resource may be required to satisfy the demand.